1. Field of the Invention
The present invention relates to a method for manufacturing a butadiene-propylene copolymer. More precisely, it relates to a method for manufacturing a novel, elastic butadienepropylene random copolymer having a high molecular weight for use in the rubber industry.
The propylene unit in the polymer chain of the random copolymer obtained by the present invention is statistically distributed in proportion to its content (3 to 45 mol%) and butadiene units are bonded more than 60% in the form of cis-1,4 configuration.
2. Description of the Prior Art
In the rubber industry, the demand for rubber having high elasticity and excellent resistance to abrasion and thermal aging is increasing.
A butadiene propylene copolymer having random and statistical distribution of both monomer units is expected to be an excellent rubber to fulfill the demand as described above, whose properties could not be attained by conventional ethylene-propylene rubber or cis-1,4-polybutadiene.
The copolymerization of diolefin and .alpha.-olefin by Ziegler type catalysts has been attempted by several investigators.
Conventional Ziegler catalysts were found by Suminoe et al. to give a block copolymer of butadiene and propylene (T. Suminoe, N. Yamazaki and S. Kanbara; Kobunshi Kagaku, 20, 461, 1963).
Ishizuka et al. disclosed the method of preparing a butadiene propylene random copolymer by use of a catalyst prepared from titanium chloride or bromide and trialkylaluminum modified with a high molecular weight polyether having a polymerization degree of greater than 9 (U.S. Pat. No. 3 590 624).
However, the Examples of the disclosure have shown that a block copolymer or homopolymers of both monomers were partly produced in addition to a random copolymer by this method.
A highly alternating copolymer of butadiene with an .alpha.-olefin was prepared by Kawasaki et al. by use of a vanadium compound or titanium compound mixed with aluminum alkyl at an extremely low temperature to avoid the aggregation of the catalyst (U.S. Pat. Nos. 3 652 518, 3 652 519 and 3 714 133). In this alternating copolymer, the butadiene unit and the propylene unit are bonded alternately and the contents of both monomer units are about 50 mol% respectively.
That is quite different from the random copolymer of the present invention, whose propylene content is within the range of 3 to 45 mol%.